The invention relates to a keyboard comprising at least one key mounted in connection with a circuit board and including a light source. The key includes a key cap and, between the key cap and the circuit board, there is a body part that diffusively transmits the light for the key. The light source is arranged to conduct light into the body part and to illuminate the key.
In prior art keys, the key body usually is a molding plastic part with its bottom surface coated with an electrically conducting material. The coating material must be elastic, and its resistance from one edge of the coated area to the other edge has to be between 100 and 1,000 ohms. Such a coating considerably increases the cost of the otherwise cheap molded plastic part, and thus it increases the manufacturing costs of the keyboard.
When the key is depressed, the bottom surface of the body part will hit a contact area comprising two halves on the surface of the circuit board. These halves are also coated with an electrically conducting material. When the bottom surface of the key body part establishes a short circuit between the halves of the contact area, the depression of the key can be electronically detected. The addition of the material of the contact halves decreases the yield of the circuit boards and increases their manufacturing costs. In particular, the alignment difficulties at either end of the keyboard will cause material losses. In addition, the electrical contact is exposed to humidity and chemical aging processes and to rubbish entering the operating device.
The illumination of the key is, according to prior art, realized so that on the surface of the circuit board there are light emitting diodes (LED) illuminating the keyboard. The light is conducted from the LEDs through light conductors to the body part proper and the key. Generally one LED illuminates several keys at the same time, e.g. so that 20 keys are illuminated by 6 LEDs. As a consequence, the luminance of the light will vary from key to key. In addition the luminance value will be low. In prior art arrangement, it is very difficult to realize a light conductor network, which would evenly distribute the light to every key.